A U.S. missile strike on an air base near Homs on Friday is not believed to have caused "big human casualties" but has caused material damage, Homs Governor Talal Barazi told Reuters.

"I believe - God willing - that the human casualties are not big, but there is material damage.

"We hope there are not many victims and martyrs," he said by telephone.

He said rescue and fire-fighting operations had been going on for two hours.